A major contributing factor in progression of HIV disease to AIDS is the loss of functional CD4+ T cells that provide critical helper activity for humoral and cell-mediated immune responses. It appears that only a small, proportion of T cell loss is attributable to lytic infection. Rather most T cells are stimulated to become antiger irresponsive and/or to undergo apoptosis by a mechanism involving of HIV gp120-induced CD4-mediatec transmembrane signal transduction. This response can apparently be induced by soluble gp120, gpl2( aggregated by endogenous anti-gp 120 antibodies, HTV itself or infected cells expressing cell surface gp120. The molecular mechanisms underlying CD4 transduction of "inhibitory" signals is unknown. Experiments proposed in this application seek to address the molecular basis and functional consequences of gp120 stimulated CD4 signaling. Studies conducted during the previous period of support have led to a quantum leap in our understanding of the inhibitory signaling circuitry activated by gp120. They show that the SH2 domain containing jnositol 5 Phosphatase SHIP and its effector, the adapter Downstream Qf Kiinase (Dok), which were previously implicate in inhibitory FcyRIIB signaling, are associated with CD4fLck complexes and are phosphorylated upon CD4 aggregation by gp 120. Further, findings indicate that linker functions of SHIP and Dok, and enzymatic activity of SHIP are activated by this stimulation. Finally, studies using T cells from SHIP knockout mice demonstrate that SI-HP is required for optimal CD4-mediated inhibition of T cell activation. Towards elucidation of this circuitiy, we propose dissection of intermolecular interactions among CD4/Lck, SHIP and Dok, and the regulatory function of these interactions (aim 1). Further studies wifi define the site within TCR signaling cascades that are the targets of SHIP and Dok (aim 2). In aim 3 we propose use of the SCID-hu thyfliv model to directly analyze the role of SHIP and Dok in HIV- 1 induced immunopathology ir human T cells. Finally, we will address the role of SHIP and Dok in progression of HIV disease to AIDS (aim 4). The studies will employ biochemical assays of signal transduction, in conjunction with gene mutation anc deletion, and human-mouse chimera to define structure-function relationships in the pathway. Finally, HIV infected patients will be employed to assess the possibility that mutations/allotypic differences which rendei this inhibitory circuit inactive may result in long term non-progression. The studies may validate SHIP as target for discovery of therapeutic agents for AIDS.